Car driven about 200 miles a year. Started getting a lil'
scratchy in 3rd about a year later when speed-shifting.
Now notchy (scratchy's big brother) when hit hard, now
scratchy even when shifted gingerly.

Pointing no fingers & "blaming" no one or brand.

What does AGE recommend?
Are the M23Ws better suited for shifting hard?
Are better/improved synchros available since 2004?

I appreciate the boost!
This is Nathan from AG. Back in 04, you probably dealt with my Chief Engineer George, or our Manufacturing Engineer Bill.

Assuming your shifter linkage is still adjusted tight and in good repair; there have been a lot of improvements over the past 13 years. I don't think you *NEED* an M23 series; but you probably could use our tighter fitting hubs and lighter sliding clutches. A new 3rd gear (along with the new slider) should cure your scratch. Slightly less likely would be the cast iron shift forks everyone used back then; we've gone to American-made cast steel ones. Even less likely would be wear in the sidecover assembly.
I'd also mention I hope you changed your oil since you bought this If you want the most recent oil recommendations, just say so.

If you don't want to do the work yourself, I'd be glad to go through it here, or try to find you a shop local to you.
I'm glad she's served you well for over a decade!
Contact me privately if you want to talk about service work and prices.
Anything else I can do for you Sir?